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The present invention relates generally to millimeter wave radar, and more specifically to a millimeter wave radar system configured to reduce adverse effects of process misalignment.
In recent years, millimeter wave radar has been increasingly employed in automotive vehicles as part of Adaptive Cruise Control (ACC) systems. A conventional millimeter wave radar system adapted for ACC applications includes an antenna assembly such as a microstrip antenna array assembly that can be mounted on an automotive vehicle. The microstrip antenna array assembly is configured to transmit one or more directional beams to scan a field of view ahead of the vehicle, and receive one or more electromagnetic waves reflected from objects within the field of view to collect certain information about the objects. For example, the collected information may include data on the relative speed, direction, and/or distance of the objects in a roadway ahead of the vehicle. Further, the ACC system may use that information to decide whether to alert a driver of the vehicle to a particular obstacle in the roadway and/or automatically change the speed of the vehicle to prevent a collision with the obstacle.
The microstrip antenna array assembly included in the conventional millimeter wave radar system comprises a channel formed in a surface of a backing plate, and a microstrip antenna array assembly including a microstrip antenna array and a ground plane with a dielectric substrate disposed therebetween. The channel formed in the backing plate surface and the adjacent ground plane form a waveguide. The ground plane has a plurality of slots formed therethrough such that junctions of the waveguide, the slots, and the microstrip antenna array define a plurality of respective waveguide-slot-microstrip transitions. The conventional millimeter wave radar system further includes a transmitter/receiver unit configured to transmit electromagnetic wave energy to the waveguide for subsequent transfer to the microstrip antenna array via the waveguide-slot-microstrip transitions, and receive electromagnetic wave energy from the waveguide via the microstrip antenna array and the waveguide-slot-microstrip transitions.
One drawback of the conventional millimeter wave radar system is that it has close manufacturing tolerances, which can lead to misalignment between the channel forming the base of the waveguide and the slots in the ground plane. Such misalignment can cause increased sidelobe levels in radiation fields produced by the millimeter wave radar system. This is particularly problematic in ACC systems because increased sidelobe levels can reduce the sensitivity of the system, and therefore compromise the validity of information collected on objects in a roadway ahead of a vehicle. As a result, the ACC system may make improper decisions regarding whether to alert a driver of the vehicle and/or automatically change the speed of the vehicle to prevent a collision with an obstacle in the roadway.
It would therefore be desirable to have a millimeter wave radar system that can be employed in automotive ACC applications. Such a millimeter wave radar system would be configured to reduce the adverse effects of misalignment in the process for manufacturing the system.
In accordance with the present invention, a millimeter wave radar system that is less sensitive to process misalignment is disclosed. Benefits of the presently disclosed system are achieved by placing slot radiators in a ground plane disposed between a microstrip antenna array and a waveguide channel so that the slots are on the same side of the longitudinal centerline of a waveguide wall.
In one embodiment, the millimeter wave radar system includes at least one channel formed in a metal backing plate and an adjacent microstrip antenna array assembly. The microstrip antenna array assembly includes a substantially planar circuit board, a single microstrip antenna array disposed on a first surface of the circuit board, and a ground plane disposed along a second circuit board surface such that a dielectric substrate of the circuit board is between the microstrip antenna array and the ground plane. The combination of the microstrip antenna array, the dielectric substrate, and the ground plane forms a plurality of microstrip transmission lines.
The ground plane is mounted to the metal backing plate comprising the at least one channel to form at least one waveguide. A portion of the ground plane comprising a wall of the waveguide has a plurality of slots formed therethrough. The plurality of slots is transversely located relative to the microstrip transmission lines and longitudinally located relative to the waveguide, thereby forming a corresponding plurality of waveguide-slot-microstrip transitions for transferring electromagnetic wave energy between the microstrip transmission lines and the waveguide.
The plurality of slots is placed on the same side of the longitudinal centerline of the waveguide wall. In a preferred embodiment, the plurality of slots comprises collinear slots having spacing equal to about one wavelength at the operating frequency of the system to assure that the electromagnetic wave energies transferred via the waveguide-slot-microstrip transitions are inphase.
In another embodiment, the plurality of collinear slots has spacing equal to less than one wavelength at the operating frequency of the system. Conductive microstrips included in the microstrip antenna array are configured to provide sufficient phase shift to assure that the electromagnetic wave energies transferred to the microstrip antenna array are in-phase.
By placing the plurality of slots on the same side of the longitudinal centerline of the waveguide wall, manufacturing tolerances of the millimeter wave radar system are relaxed, thereby reducing adverse affects of process misalignment, e.g., increased sidelobe levels in radiation fields.
Other features, functions, and aspects of the invention will be evident from the Detailed Description of the Invention that follows.